The invention relates to a compressor of a turbocharger, the compression pipe of which is connected to the intake pipe thereof via an overrun air recirculation valve, and to a turbocharger and a motor vehicle having a compressor of said type.
The diesel or Otto-cycle engine of numerous motor vehicles has a turbocharger, in which inducted fresh air is supplied under pressure to the combustion chamber by means of a compressor which is driven by the exhaust-gas flow, that is to say the injected fuel mixture is “supercharged”. By means of the supercharging of the fuel mixture with pressurized fresh air—and the thus increased oxygen content—it is possible even at low engine speeds for a high torque to be provided by virtue of the combustion process being promoted.
In the case of some turbocharged engines, however, so-called “turbo lag” arises, which occurs if, after a release of the accelerator pedal, the accelerator pedal is quickly intensely depressed again. If, in the case of such compressors, the accelerator pedal is released, and thus the throttle flap is closed, in a sudden manner, a high dynamic pressure builds up downstream of the compressor, which cannot escape because the path to the intake pipe is closed by means of the throttle flap. The corresponding surging of the turbocharger gives rise to such an intense counterpressure at the compressor wheel that the latter is intensely braked.
If the driver then suddenly opens the throttle flap again by depressing the accelerator pedal again, the counterpressure immediately intensely drops. Nevertheless, the compressor wheel of the turbocharger has already been braked, such that a certain amount of time is required until the torque boosted by the turbocharger and expected by the driver is available again.
To avoid the surging of the turbocharger that is the cause of turbo-lag in overrun operation, it has in the meantime been the approach, in the compressor of many turbocharged engines, to install an overrun air recirculation valve (also referred to as overrun cut-off valve, pop-off valve or snifter valve), which can open up a return-flow duct between the compression pipe and the intake pipe of the turbocharger during overrun operation. With the fresh-air circuit thus formed, braking of the compressor wheel is avoided, such that, even in the case of the accelerator pedal being depressed again, the full charge pressure is available immediately.
In the case of such compressors, it has however been found that the ambient air flowing at high pressure through the return-flow duct, which ambient air has at least initially already been compressed, gives rise to disturbing flow noise when it enters the intake pipe again.
It is consequently the object of the present invention to provide a compressor of a turbocharger which exhibits less noise generation during overrun operation.
This and other objects are achieved according to the invention by a compressor of a turbocharger, the compression pipe of which is connected to the intake pipe thereof via a return-flow duct in which there is arranged an overrun air recirculation valve for controlling the return flow of already-compressed fresh air. Here, the return-flow duct opens into a groove of an intake connector receptacle of the compressor, and, on an intake connector of the intake pipe, there is arranged at least one return-flow opening, which adjoins the groove, to an interior space of the intake pipe.
The invention is based on the underlying concept whereby, during overrun operation, with the overrun air recirculation valve open, fresh air flowing back through the return-flow duct is firstly diverted and/or distributed before it can flow into the intake pipe. In interaction with the groove of the intake connector receptacle and the intake connector inserted therein, such a diversion and/or distribution may preferably occur at one or more return-flow openings which are arranged in the circumference at a location other than at the return-flow duct.
It is also possible to avoid a reduction in efficiency of the compressor, such as can arise, without the invention, at the inlet of the return-flow duct from turbulence on one side upstream of the compressor wheel and associated pressure losses and poor center values.
To optimize the distribution of the return flow of fresh air in the groove, the groove is, according to one refinement, arranged along the entire circumference of the intake connector receptacle. The groove is then preferably formed as a ring-shaped groove, preferably proceeding from an inner circumferential surface of the intake connector receptacle. Typically, a ring-shaped groove of said type is provided already in a casting mold of the compressor or of the turbocharger, though it may also be formed from a cylindrical or conical circumferential surface by a cutting procedure.
To ensure that the intake connector is received in the intake connector receptacle easily and in a simultaneously reliable manner, it is also possible, in an alternative embodiment, for the groove to be arranged only along a part of the circumference of the intake connector receptacle.
Undesired flow noise, as in the case of the known compressors mentioned in the introduction, is promoted in particular by an increased return flow, a relatively high pressure, a relatively high speed of the return flow, and/or by a small outlet cross section. To avoid this, in one refinement, the intake connector has, in particular in the region of the groove, more than one return-flow opening, in particular two, three or four. These are advantageously of such a size that they utilize the entire opening of the groove in the intake connector receptacle along a longitudinal axis of the compressor.
If multiple return-flow openings are provided, these are preferably arranged, with respect to the circumference of the intake connector, at locations with substantially the same pressure potential of the inducted fresh air during operation of the turbocharger. So-called “crosstalk”, in the case of which air flows in the groove from a return-flow opening with relatively high pressure potential to a return-flow opening with relatively low pressure potential, can thus be avoided, along with the associated pressure losses.
To minimize swirling or turbulence when the return flow and the intake flow impinge on one another, in one refinement, the intake connector has a larger inner diameter in the region of the return-flow opening(s) than in a region which is situated adjacent along the axis of rotation of a compressor wheel of the compressor and which is remote from the compressor wheel.
This effect can be further intensified in that, in one refinement, the intake connector has a separation edge, in particular a flow separation edge, upstream of the return-flow opening with respect to a main intake direction in the intake pipe, by which separation edge the fresh-air flow is preferably diverted away from the delimitation of an inner cross section of the intake connector.
To extract kinetic energy from the return flow, the return-flow duct is arranged so as to be at least partially offset with respect to a return-flow opening, in particular circumferentially offset.
To permit simple and/or inexpensive production of the compressor, a return-flow opening is formed with a bore in a wall of the intake connector, or is provided already in a casting mold for producing the intake connector.
To make the convergence of the return flow and of the intake flow more expedient from a flow aspect, in particular less turbulent, a return-flow opening is, at least over a part of its radial extent, formed so as to be open toward a compressor-wheel-side face side of the intake connector.
According to a further aspect of the invention, a turbocharger is provided which has a compressor within the meaning of the invention. Likewise provided is a motor vehicle which has a turbocharger of said type.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.